Short cycle annealing process for producing malleable iron



March 21, 1933- I. R. VALENTINE 90 SHORT CYCLE ANNEALING PROCESS FOR PRODUCING MALLBABLE IRON Filed April 9, 1930 Fig.\

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Patented Mar. 21, 1933 UNITED STATES PATENT OFFICE IRVING R VALENTINE, F ERIE, PENNSYLVANIA, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK Application filed April 9,

The present invention relates to a short cycle annealing process for producing malleable cast iron and is a continuation in part of my copending applications Serial N 0. 437,823,

filed March 21, 1930, and Serial N 0. 293,276.

filed July 16, 1928, now Patent N 0. 1,830,630.

It is an object of the present inventlon to provide an improved short cycle annealing process for producing malleable iron.

The novel features which are characteristic of my invention are set forth with particularity in the appendedclaims. The invention itself however will best be understood from reference to the following specification when considered in connection with the accompanying drawing in which Fig. 1 shows iagrammatically a heat-time cycle which may be employed in carrying my invention into effect; Fig. 2 shows diagrammatically an arrangement of high and low temperature furnaces which may be employed in the process, while Fig. 3 is a cross sectional view of a low temperature elevator type electric furnace which may be employed in the process,

the heater elements and elevator portion of the furnace being omitted.

. In carrying out my invention, a five or six ton load of white iron castings of normal composition is placed in an electric, elevatortype furnace 1, and heated in a few hours to a temperature of about 900 C. as indicated in Fig. 1. The castings are held at this temperature for a few'hours and then raised in about 1 hour to a temperature of about 980 0., maintained at the latter temperature for about 2 hours, then raised to 1000 C., maintained at that temperature for about 2 hours and then raised to a temperature of about 1020 C., and maintained at that temperature 40 for a few hours. Ordinarily, it is sufficient to heat the castings to a temperature of about 1000 G. Since the lower portion of the load is usually somewhat cooler than the u per portion, it is sometimes desirable to heat those castings which are in the upper portion of the furnace to a temperature of about 1020 C. in order to ensure that all the castings in the load are heated to at least 1000 To ensure a proper distribution of the heat in the furnace, a pair of fans 2 and 3 -manner, about 6 to 11 h 1930. Serial No. 442,921.

may be mounted at opposite ends of the furnace and driven by means of electric motors, not shown, which may be mounted on the outer portion of the furnace walls.

e11 the castings have been heated to a temperature of about 1000 to 1020 C. for a cementite in the castings has gone into solid solution, the load is transferred over tracks 4 to a point directly underneath low temperature furnace 5 and raised into the latter furnace. Furnace 5 is an electric furnace of the elevator type and is heated to a temperature of about 720 C.

. The castings, when introduced into the '65 furnace 5, should have a temperature of at least 860 C. or higher. To bring the temperature of the castings down quickly to 7 20 C. without quenching, the load is lowered at 'ntervals from furnace 5 into the air and then 7 returned to the furnace. Ordinarily, the time required to drop the load from the furnace will vary from about 10 to about 60 seconds while about 1 minutes will be required to return it to the furnace. When the load is lowered, it may be returned immediately to the furnace, or, if desired, allowed to stand in air for a period of time which may vary from about 2 minutes at the start to about 10 seconds at the end of the cooling process. The intervals during which the load is lowered from the furnace may be from about 15 minutes to 1 hour apart, preferably one-half hour.

en the castings are cooled in the above ours are required to bring the temperature of the castings down to 720 C. At this point in the annealing cycle the castings may have a tensile strength of 61,300 lbs. per square inch, and an elongation of about 10% in 2 inches. The temperatureof the castin s is then raised slowly in about 2 ho rs to At this point in the cycle 1t will be found that the tensile been'reduced to bs. per square inch but that has been increased to about I have found it desirable to maintain the castings at a temperature of about 730 C.

i the latter temperature for about 2 or 3 hours.

I by dropping the ed in the chamber 8 adjacent When the load of castin s,

' tionary measure Heating the castings at 730 0. and 720 0. for a few hours produces little change in either the tensile strength or elongation, these steps being employed merely as a precauto ensure that the castings will have normal malleable cast iron characteristics.

Instead of cooling the castings to 720 0. load at intervals from the furnace, I may employ an electric elevatortype furnace 6 provided with rapid cooling features. To produce the desired cooling effeet the furnace is provided with a duct 7 having an enlarged chamber 8. 9 is mounted in chamber 5 and provided with a series of pipes or fines 10. These flues are surrounded with a cooling fluid, for example water, supplied to the container 9 through an inlet pipe 11. A fan or blower 12 mountthe flues 10, is driven from an electric motor 13 mounted on'the outside of the furnace walls. Fan 12 draws the hot furnace gases through the air duct 7 and flues 10 where they are cooled and'then returned to the the furnace.

Furnace 6 is normally heated to 720 0. which has been heated to about 1000 in furnace 1, is transferred to furnace 6, the load raises the temperature of the furnace to at least 860 0. Circulation of the hot furnace gases through duct 7 and flues 10 of the cooling apparatus quickly reduces the temperature of the castings to 720 0. 'When the castin s are cooled in furnace 6, the time required to reduce the temperature of the castings to 720 0. is approximately 6 hours.

In Fig. 2 of the drawing, I have shown a battery, of high temperature furnaces 1 interconnected with low temperature furnaces 5 by means of tracks and turntable 14. While a single high temperature furnace and a single low temperature furnace are sufficient for carrying out my process, it will sometimes be found desirable to employ a plurality of each type of furnace rather than one of each type owing heating the castings in the high and low temerature furnaces.

What I claimas new and desire to secure by Letters Patent of the United States, is:

1. The method of producing malleable cast iron which comprises heating white cast iron at an elevated temperature for a period of time long enough to cause the cementite in the iron to gointo solid solution, cooling the heating chamber of casting in about 6 to 11 hours to a temperature of about 720 0. and'raising the temperature of the casting to 730 0. in a'relatively short time and maintaining the casting at 730 0. for a few hours.

A container riod of time not 2. The method of producing malleable cast iron which comprises heating white cast iron at an elevated temperature for a period 0 time long enough to cause the cementite in the iron to go into solid solution, cooling the casting to a temperature of about 720 0., raisin the temperature of the casting to about 0. in a relatively short time, and maintaining the casting at the perature for a few hours and then reducing the temperature abruptly to about 720 0., and maintaining the castin at the latter temperature fora relatively s ort time.

3. The method of producing malleable cast iron which comprises heating a white iron casting for about 12 hours at a temperature increasing gradually from about 900 0. to about 1000 0., cooling said casting in a period of time not less than 6 hours to a temperature zone having an upper limit of about 750 0. and a lower limit of about 700 0., and maintaining the casting in said temperature zone for a few hours.

4. The method of producing malleable cast iron which comprises heating a white iron casting for about 12h-ours at a temperature increasing gradually from about 900 0. to about 1000 0., cooling said casting in a peless than 6 hours toa temperature zone having an upper limit of about 750 0. and a lower limit of'about 700 ma ntaining the temperature substantially constant in said zone ing said temperature a few degrees and againmaintaining it constant for a few hours.

5. The method of producing malleable cast iron which comprises heating a white iron casting at a temperature in the neighborhood of 900 0. to 1000 0. for a period of time varying from about 4 to about 13 hours, cooling said casting in about 6 to 11 hours to a temperature below 750 heating the casting at about 730 0. for a few hours and then heating the casting at about 720 0. for a few hours. i

In witness whereof, I have hereunto set my hand this 7 day of April 1930.

IRVING R. VALENTINE.

to the difference in time required in r latter temfor a few hours, chang-- 0. but above 700 0., 

